The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for establishing layer-2 entities for D2D communication system, the method comprising: configuring a sidelink radio bearer over which the UE transmits data to a peer UE; establishing RLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol) entities for the sidelink radio bearer by selecting one of configuration information sets, wherein each configuration information set is identified by each configuration information index; and transmitting configuration information of the sidelink radio bearer via a sidelink to the peer UE, wherein the UE is directly connected to the peer UE via the sidelink.